(1) Field of the Invention
This invention relates to gas generation, and more particularly to gas generation systems useful for inflation purposes.
(2) Description of the Related Art
Rapid deflagrating cord (RDC), sometimes erroneously identified as rapid detonating cord has been in common use in the explosives industry as a transfer line for igniting explosives. Detonating cord (detcord) has been used extensively as a transfer line and as an explosive (e.g., for cutting structural elements). Both RDC and detcord comprise a sheath containing an explosive (commonly identified as a “pyrotechnic” in the case of RDC). Detcord typically comprises a plastic or cloth sleeve containing a high explosive charge. When ignited at one end, detcord burns via propagation of a detonating shock wave. The shock wave moves through the explosive at a velocity greater than the speed of sound in the explosive (nearly always in excess of about 2000 ml/s and typically 5000–7000 m/s) and ignites the unreacted explosive through which it passes. With RDC, burning is via deflagration, a high velocity subsonic propagation (typically less than 2000 m/s). With RDC, thermal energy is transferred from the reacted explosive to the unreacted explosive primarily via conduction. With detcord and RDC, the combustion involves self-contained oxygen in the explosive charge.
RDC has been used as a component in gas generators. RDC can typically be ignited via the output of a conventional automotive airbag initiator (e.g., one containing a charge of 35 mg zirconium potassium perchlorate (ZPP) or its equivalent). The output of such an initiator is not reliably capable of directly igniting detcord. Detcord requires a detonator to provide the initial energy necessary to induce ignition of the detcord.
U.S. Pat. No. 6,062,143 of Grace et al. identifies a distributed charge inflator (DCI). The application identifies use of an electronic squib (commonly used in automotive airbag inflators) to ignite a core of ignition material such as RDC or mild detonating fuse (MDF). The presence of a gas-generating layer or coating on the core is also identified.
U.S. Pat. No. 5,967,550 of Shirk et al. identifies a staged pyrotechnic air bag inflator. A housing defines a chamber with an end-burning pyrotechnic charge The charge has a first predetermined burn rate at a first location along the length of the chamber and a different second predetermined burn rate at a second location along the length of the chamber spaced apart from the first location. The second burn rate may be effective to maintain inflation of the air bag over a desired interval.